A large number of balloon angioplasty devices exist for relieving arterial stenoses by compression of the stenosis. Balloon angioplasty devices afford numerous advantages over alternative methods and apparatus which can be used for removing stenoses that are formed when plaque builds up in a patient's arteries. Foremost among these advantages is that open heart bypass surgery can often be avoided by using angioplasty surgical techniques to relieve stenoses in arteries which supply the heart. It is preferable to avoid open heart bypass surgery when possible because such surgery, as is well known, is relatively invasive and entails a relatively long post-operative recovery period. Accordingly, it is preferable to use relatively simpler angioplasty surgical procedures when such procedures are feasible. In angioplasty surgery, an inflatable balloon which is initially in a collapsed configuration is attached to a catheter, and the catheter is connected to a source of fluid. The balloon is then positioned at the desired location in the affected artery by inserting the balloon through an appropriate major artery, e.g. the femoral or carotid artery, until the balloon has been positioned next to the stenosis to be treated. Once the balloon has been properly positioned, fluid is infused into the balloon through the catheter to inflate and expand the balloon within the artery. As the balloon expands, it dilates the lumen of the artery and compresses the stenosis. Upon being compressed, the stenosis may break up or flatten out against the arterial wall. The balloon is subsequently deflated and, once in its collapsed configuration, it is either withdrawn from the artery or placed across another stenosis, to restore normal blood flow through the artery.
To effectively expand the lumen and compress the stenosis, it is desirable that the balloon be reliably inflatable to a relatively large diameter when the balloon is infused with fluid. This is so in order to evenly expand the balloon within the affected artery to evenly dilate the vessel, compress and hence compromise the stenosis. Also, it is desirable that the balloon be reliably collapsible to a minimal, radially compact cross sectional shape incident to balloon insertion and withdrawal. This is to facilitate insertion and withdrawal of the balloon in artery. While existing angioplasty balloons are collapsible, it is unfortunately the case that many existing balloons typically cannot be reliably collapsed, i.e., deflated, to a radially compact minimal cross section after inflation. Instead, they often flatten when deflated. This flattening increases interference between the flattened balloon and the arterial wall during balloon withdrawal or when being placed across a second stenosis. Consequently, a flattened balloon can be relatively difficult to withdraw from an artery.
Existing devices attempt to provide symmetrically collapsible structures by a variety of methods. For example, a venous catheter is disclosed in U.S. Pat. No. 4,406,656 to Hattler, et al. which has multiple collapsible lumens that are intended to collapse around a central non-collapsible lumen. For the Hattler, et al. device, the central lumen retains its shape when the catheter is collapsed. Additionally, a dilatation catheter is disclosed in U.S. Pat. No. 4,896,669 to Bhate, et al., which has a crimped outer tubular balloon portion and an inner catheter extending lengthwise through the crimped outer balloon portion. With this combination, the Bhate, et al. device attempts to provide a balloon that collapses to a small cross section by crimping portions of the outer balloon to guide the non-crimped portion of the outer balloon around the inner catheter when the balloon is collapsed.
The Hattler, et al. device is not intended for use in angioplasty procedures and devices such as Bhate, et al. have scored, interconnected, crimped, or pre-folded portions of the balloon that are weakened relative to other portions of balloon. Scored or crimped devices are, unfortunately, susceptible to leaking or tearing when the balloon is inflated at the relatively high inflation pressures (upwards of four atmospheres) that are typically used in angioplasty procedures. Also, such devices do not always provide a balloon which can be reliably collapsed to a small, compact cross sectional shape. Instead, the balloons may occasionally flatten when deflated. The present invention recognizes that it is possible to provide an angioplasty balloon which reliably collapsed into a minimal, compact cross section without weakening portions of the balloon.
Accordingly, it is an object of the present invention to provide a collapsible angioplasty balloon which can be reliably collapsed into a compact minimal cross sectional configuration. Another object of the present invention is to provide a collapsible angioplasty balloon that can be reliably inflated into a radially-symmetrical, relatively large cross sectional configuration. It is also an object of the present invention to provide a collapsible angioplasty balloon all of the portions of which have a substantially high resistance to leaking and tearing when the balloon is inflated. A further object of the present invention to provide a collapsible angioplasty balloon which is relatively easy to use and comparatively cost-effective to manufacture.